[C320-list] Holding Tank Flooding

[Jeff Hare]

I would not be surprised if you could sink your boat this way depending on how the hose leading from the head to the tank is routed and how good your head's duckbill is.  If you pump out with the macerator thru-hull open and the head vent is at all clogged, the vacuum will pull seawater in through the macerator pump and water out of the head and could set up a siphon and will likely slowly fill your tank to the water line.  I presume but don't know whether the rim of the head is above the water line.  If not, the boat can be sunk this way.

Bottom line is that the macerator line does not have a vacuum breaker in it, so it can never be left open.  When your tank is being pumped out through the deck fitting, I believe you always want that valve closed anyway.

-Jeff

-----Original Message-----
From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Kaare Wold
Sent: Tuesday, July 19, 2016 4:25 PM
To: C320-List at Catalina320.com
Subject: [C320-list] Holding Tank Flooding

Skippers,  Recently we noticed that our holding tank fills with water when at rest at the dock.  At first, thought our dock attendants failed to pump out.  We have an AccuGage digital monitor on all tanks.  Love that setup! 
We had the tank pumped, while we were present,  and as the tank was being pumped out, I could see the AccuGage digital level drop from 3/4 to 1/2 down to empty. A couple days later, it was back to 3/4 full without any personal use whatsoever.  The macerator thruhull had been open all the time, although we never use that device.  All thruhull are opened for winter layup and I never closed it after spring launch.  I now closed the thruhull, had the tank pumped out again and.....bingo...,  the tank remained empty.  Any ideas 
from our knowledgeable group???   Could there be a check valve in the 
macerator pump that is leaking?    Looking for some suggestions or comments 
from someone that may have experienced the same problem.  Thanks to all for your comments.
Kaare & Mary Wold
Sheet Music, #945  Sturgeon Bay, WI